Although polyolefins typified by polyethylene and polypropylene have been used versatilely, they are not suitable for all uses. Polyolefins are inherently non-polar, and therefore inferior in the properties such as adhesiveness, and persistence, print performance and affinity of dyes, and limited in their usefulness. However, it is known that such properties can be remarkably improved in functionalized polyolefins obtained by incorporating a small amount of polar functional groups in polyolefins.
In an effort to expand the application range of polyolefins, methods for incorporating polar functional groups into polyolefins have been reported (Non-patent documents 1, 2 and the like). Among these methods, the most direct method is to copolymerize olefin monomers with industrially useful polar vinyl monomers as shown in the following formula.

Coordination-insertion polymerization (coordination-addition polymerization) of olefins and polar vinyl monomers using a transition metal catalyst was proposed as a useful method for synthesizing functionalized polyolefins having a predetermined polymer structure, molecular weight distribution and amount of comonomer to be incorporated. As a late transition metal complex as a catalyst for coordination-insertion polymerization of olefins and polar vinyl monomers, the most successful one to date is the catalyst in which α-diimine or phosphine sulfonate ion is coordinated (Patent Document 1, Non-patent Documents 3 and 4). Generally, a highly-linear microstructure of polymer can be obtained by a palladium and nickel catalyst in which a phosphine-sulfonate ion is coordinated. Meanwhile, a palladium and nickel catalyst in which α-diimine is coordinated serves as a catalyst for forming a highly-branched polymer. Among these two important catalysts, it has been reported that the catalyst in which a phosphine-sulfonate ion is coordinated exhibits much higher activity in the copolymerization with polar vinyl monomers such as vinyl acetate, acrylonitrile, vinyl chloride and vinyl ether, compared to the catalyst in which α-diimine is coordinated (Non-patent Documents 5, 6 and the like).
However, a transition metal complex in which phosphine-sulfonate ion is coordinated has not yet been put to practical use.
Also, a method for copolymerizing ethylene and methyl acrylate using a nickel complex having an iminoamide ligand has been proposed (Patent Document 2), but the method has not yet been put to practical use, either.